@article{Heckathorn2002,
author = {Heckathorn, D.D. and Semaan, S. and Broadhead, R.S. and Hughes, J.J.},
title= {Extensions of respondent-driven sampling: A new approach to the study of injection drug users aged 18–25},
year = {2002},
doi = {10.1023/A:1014528612685},
journal = {AIDS & Behavior },
volume = {6},
number = {1},
pages = {55--67},
}